Stimulator for treatment of back pain utilizing feedback

ABSTRACT

Apparatus and methods for treating back pain are provided, in which an implantable stimulator is configured to communicate with an external control system, the implantable stimulator providing a neuromuscular electrical stimulation therapy designed to cause muscle contraction to rehabilitate the muscle, restore neural drive and restore spinal stability; the implantable stimulator further including one or more of a number of additional therapeutic modalities, including a module that provides analgesic stimulation; a module that monitors muscle performance and adjusts the muscle stimulation regime; and/or a module that provides longer term pain relief by selectively and repeatedly ablating nerve fibers. In an alternative embodiment, a standalone implantable RF ablation system is described.

I. REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 15/853,543, Dec. 22, 2017, now U.S. Pat. No. 10,661,078, which is acontinuation application of U.S. application Ser. No. 14/849,478, filedSep. 9, 2015, now U.S. Pat. No. 9,861,811, which is a continuationapplication of U.S. application Ser. No. 13/045,421, filed Mar. 10,2011, now U.S. Pat. No. 9,248,278, which claims the benefit of priorityof U.S. provisional application Ser. No. 61/339,957, filed Mar. 11,2010, the entire contents of each of which are incorporated herein byreference in their entireties.

II. FIELD OF THE INVENTION

This application relates to apparatus and methods for treating back painby combining circuitry for providing neuro-muscular electricalstimulation (NMES) therapy with circuitry for providing analgesicstimulation, performance monitoring and feedback, and/or selectiveablation.

III. BACKGROUND OF THE INVENTION

The human back is a complicated structure including bones, muscles,ligaments, tendons, nerves and other structures. The spinal columnconsists of interleaved vertebral bodies and intervertebral discs. Thesejoints are capable of motion in several planes includingflexion-extension, lateral bending, axial rotation, longitudinal axialdistraction-compression, anterior-posterior sagittal translation, andleft-right horizontal translation. The spine provides connection pointsfor a complex collection of muscles that are subject to both voluntaryand involuntary control.

Muscles provide mechanical stability to the spinal column. Crosssectional images of the spine demonstrate that the total area of thecross sections of the muscles surrounding the spinal column is muchlarger than the spinal column itself. Additionally, the muscles havemuch larger lever arms than those of the intervertebral disc andligaments. The motor control system sends signals down nerves toactivate the muscles of the back in concert to maintain spine stability.

The multifidus is the largest and most medial of the lumbar backmuscles. It consists of a repeating series of fascicles which stem fromthe laminae and spinous processes of the vertebrae, and exhibit asubstantially similar pattern of attachments caudally. These fasciclesare arranged in five overlapping groups such that each of the fivelumbar vertebrae gives rise to one of these groups. At each segmentallevel, a fascicle arises from the base and caudolateral edge of thespinous process, and several fascicles arise, by way of a common tendon,from the caudal tip of the spinous process. Although confluent with oneanother at their origin, the fascicles in each group diverge caudally toassume separate attachments to the mamillary processes, the iliac crest,and the sacrum. Some of the deep fibers of the fascicles which attach tothe mamillary processes attach to the capsules of the facet joints nextto the mamillary processes. All the fasicles arriving from the spinousprocess of a given vertebra are innervated by the medial branch of thedorsal ramus that issues from below that vertebra.

Normally, load transmission in the spinal column is painless, with themuscles acting in concert with the ligaments and bones preventingexcessive relative movements of the structures. The neutral zone is therange of intervertebral motion, measured from a neutral position, withinwhich the spinal motion is produced with a minimal internal resistance.Over time, dysfunction of the spinal stabilization system can lead toinstability and abnormal movement of the spine, resulting in overloadingof structures when the spine moves beyond its neutral zone. High loadscan lead to inflammation, disc degeneration, ligament damage, facetjoint degeneration, and muscle fatigue, all of which can result in pain.

For patients believed to have back pain due to instability, cliniciansfirst offer a group of therapies that attempts to minimize the abnormalrange of motion that leads to the pain. If this group of therapies doesnot work, then the next group of therapies aims to block the painproduced by the abnormal range of motion.

Common conservative methods of attempting to reduce abnormal motion aimto improve muscle strength and control and include core abdominalexercises, use of a stability ball, and Pilates. If conservative methodsof preventing abnormal movement are ineffective, surgical approaches maybe used.

Spinal fusion is the standard surgical treatment for chronic back pain.One or more vertebrae are surgically fused together to prevent relativemotion. Following fusion, motion is reduced across the vertebral motionsegment. Dynamic stabilization implants are intended to reduce abnormalmotion and load transmission of a spinal motion segment, without fusion.Total disc replacement and artificial nucleus prostheses also aim toimprove spine stability and load transmission while preserving motion.

If pain persists after physical therapy or surgical intervention toprevent the abnormal motion that leads to pain, few options areavailable for relief.

One option is a technique referred to as “RF rhizotomy”, in which radiofrequency (“RF”) energy is used to ablate the medial branch of thedorsal ramus that contains the afferent fibers responsible fortransmitting pain signals from the facet joint. There are severaldevices available for performing this treatment, such as those offeredby Baylis Medical Inc. (Montreal, Canada). While this technique can beeffective, it provides only short term relief as nerve fibers mayregenerate over time, and generally the procedure must be repeatedapproximately every six months to maintain effective pain control. Theelectrical parameters for RF ablation of nerves differ amongst varioussuppliers.

Another option for pain relief is Transcutaneous Electrical NerveStimulation (TENS). This technology provides low energy electricalsignals delivered via externally applied skin pad electrodes. While theexact mechanism of action is still subject to some controversy, it isgenerally believed that the electrical energy blocks the signals in theafferent nerve fibers that transmit the pain signals to the brain.

A modification to this approach is to use percutaneous wires connectedto electrodes placed nearer to the nerves (PENS or PercutaneousElectrical Nerve Stimulation). A wide variety of PENS or TENSstimulation parameters have been published, including high-frequency(HF; >10 Hz), low-frequency (LF; <10 Hz), variable-frequency (VF) andacupuncture-like (AL), which employs very low-frequency, high-amplitudestimulation. The intensity of the TENS or PENS stimulation (voltage orcurrent) is generally adjusted to a level which achieves analgesiawithout causing irritation or pain from the stimulation itself. One suchPENS device is described in U.S. Pat. No. 6,671,557.

Implantable devices for electrical stimulation of peripheral nerves forcontrol of pain have been described. For example, U.S. Pat. No.7,324,852 B2 describes an implantable electrical stimulation device witha plurality of electrodes that are implanted subcutaneously and arestimulated in a pre-determined pattern to provide pain relief.

A Spinal Cord Stimulator (SCS) is an implanted electrical stimulationdevice with one or more electrodes that are placed adjacent or near tothe spinal cord, with the goal of blocking the pain signals from beingtransmitted via the spinal cord to the brain. Although SCS wasoriginally designed and approved for radicular pain (sciatica), thetechnique is increasingly being used for lower back pain. Spinal cordstimulators may be self-powered (i.e., contain a primary battery orcell) or may include a rechargeable battery (i.e., a secondary batteryor cell), as described for example, in U.S. Pat. No. 6,516,227.

The key drawback with all of the previously known electrical stimulationtechniques that seek to block the pain signals (TENS, PENS, SCS and RFAblation of the nerves) is that relief, if obtained, is usually onlytemporary, and repeated or continuous therapies are needed.

U.S. Patent Application Publication No. US2008/0228241 to Sachs,assigned to the assignee of the present invention, describes animplanted electrical stimulation device that is designed to restoreneural drive and rehabilitate the multifidus muscle. Rather than maskingpain signals while the patient's spinal stability potentially undergoesfurther deterioration, the stimulator system described in thatapplication is designed to reduce the propensity for instability of thespinal column, which in turn is expected to reduce persistent orrecurrent pain.

While the stimulator system described in the Sachs application seeks torehabilitate the multifidus and restore neural drive, it does notprovide relief of the pain during the application of the therapy. Thus,it is possible that for some patients the effectiveness of the therapymay be hindered by the continuation of pain, which may interfere withrestoration of neural drive to the muscle or impede the patient'sability to tolerate the therapy. In addition, it is possible that as thetone of the multifidus muscle improves during use of the stimulatorsystem described in the Sachs application, it may be desirable to reducethe stimulus amplitude, frequency or duration, or stimulation intervals.

In view of the foregoing, it would be desirable to augment thestimulator system described in the Sachs application with additionaltherapeutic modalities, such as the ability to alleviate pain during andbetween muscle stimulation. It therefore may be desirable to providepain blocking stimulation to afferent nerve fibers simultaneously withmuscle stimulation pulses, or at other times.

It further may be desirable, depending upon the severity of the painexperienced by a patient and the degree to which it interferes withrehabilitation of the multifidus muscle, to provide pain blocking byselectively ablating afferent nerve fibers in conjunction with thestimulation therapy described in the Sachs application.

It also would be desirable to combine the rehabilitative stimulationtherapy described in Sachs with a capability to monitor muscleperformance during the stimulation therapy, and to adjust the appliedstimulation pulses to account for changes in the muscle tone and neuraldrive. In addition, it would be desirable to detect the duration,frequency and strength of muscle contractions to further reduce thepatient's perception of pain resulting from the muscle stimulationtherapy, for example, to avoid spasm.

IV. SUMMARY OF THE INVENTION

In view of the drawbacks of previously-known methods and apparatus fortreating back pain, the stimulator system of the present inventionprovides a neuromuscular electrical stimulation system designed torehabilitate spinal stability and restore neural drive, while providingadditional therapeutic modalities, such as the ability to alleviate painduring and between muscle stimulation intervals. In accordance with theprinciples of the present invention, an implantable neuromuscularelectrical stimulation system is provided that includes one or more of anumber of additional therapeutic modalities: a module that providedanalgesic stimulation; a module that monitors muscle performance andadjusts the muscle stimulation regime; and/or a module that provideslonger term pain relief by selectively and if necessary repeatedlyablating afferent nerve fibers.

Accordingly, one embodiment of the stimulator system of the presentinvention combines circuitry to stimulate and rehabilitate themultifidus muscle with circuitry to stimulate afferent nerves toalleviate back pain during and between muscle stimulation intervals. Theanalgesic pulse regime may be applied to afferent nerve fiberssimultaneously with muscle stimulation pulses, or at other times.

In an alternative embodiment, circuitry to stimulate and rehabilitatethe multifidus muscle may be combined with circuitry that achieves painblocking by selectively and repeatedly ablating afferent nerve fibers.

In still another embodiment, circuitry to stimulate and rehabilitate themultifidus muscle may be combined with circuitry to monitor muscleperformance during the stimulation therapy, and to adjust the appliedstimulation pulses to account for changes in the muscle tone and neuraldrive. For example, such performance feedback circuitry may detect theduration, frequency and strength of muscle contractions to furtherreduce the patient's perception of pain resulting from the musclestimulation therapy, for example, to avoid spasm.

It should be appreciated that while the foregoing additional modalitiesare described in the context of a neuromuscular electrical stimulationsystem, such as described in the foregoing Sachs application, suchmodules may be packaged separately or in other combinations forapplications other than treating back pain. For example, the RF ablationmodule may be implemented as a standalone implantable system forselectively ablating unresectable tumors located in the liver, brain,thyroid, pancreas, kidney, lung, breast, or other body structures,thereby avoiding the need for repeated reoperations. Alternatively, theRF ablation module may be combined with the analgesic stimulationmodule, such that the analgesic module provides continual pain reliefwhile the RF ablation module provides intermittent ablation of selectedafferent nerve fibers or tissue. As an additional example, the analgesicstimulator module may be combined with the performance feedback module,to provide an implantable stimulator that monitors muscle exertion andmay adjust the stimulatory regime applied to the afferent nerves tomaintain patient comfort.

The implantable electrical stimulation system of the present inventionincludes an implantable housing connected to at least one or moreelectrodes placed in appropriate anatomical locations and connected byleads to the housing. Feedthroughs (preferably hermetically sealed)connect the leads to the internal electronic circuitry. Stimulationelectrodes may be logically connected in pairs to a stimulation channeldesigned to supply the stimulation regime needed for the therapeuticmodality chosen for that electrode pair. The stimulator system may bearranged so that a different therapeutic modality may be applied toselected electrode pairs simultaneously. For example, the stimulator mayapply neuromuscular electrical stimulation to the medial branch of thedorsal ramus to effect contraction and rehabilitation of the multifidusmuscle, while simultaneously applying electrical stimulation to adifferent arrangement of electrodes placed adjacent to the spinal cordto effect spinal cord stimulation to relieve pain.

In general, the stimulator system includes an implantable housingincluding a controller, a memory, a power source (e.g., battery orcell), a telemetry system (e.g., transceiver), one or more modulescontaining therapeutic circuitries (e.g., muscle stimulation, analgesicstimulation, performance feedback or RF ablation) coupled to theelectrodes via an electrode switching circuit, and one or more sensors.The controller preferably comprises a processor, nonvolatile memory forstoring firmware, implant identification information, and system andenvironmental data, and volatile memory that serves as a buffer forcomputations and instructions during execution and firmware updating.The controller preferably is coupled to battery, transceiver, electrodeswitching circuit, therapeutic module circuitries and sensors to monitorsystem status and to activate the various therapeutic module circuitriesin accordance with the programming stored in the memory. The battery (orcell) can be a primary or secondary (rechargeable) configuration thatpreferably uses long-lasting lithium chemistry (e.g., lithium-ion orlithium polymer). If rechargeable, the battery is coupled to aninductive charging circuit, thereby enabling the battery to beperiodically coupled to an external control system for charging. A radiofrequency transceiver preferably is employed in the device fortransmitting system information to, and receiving information from, theexternal control system, including system performance data, loggedphysiological data, commands, and firmware upgrades.

The stimulator system further comprises an external control system thatmay be coupled to the stimulator housing to supply power to the powersource, to program/reprogram the controller, and to download systemparameters and data stored within the memory. The external controlsystem may be configured to transfer energy to the power source viainductive coupling. In a preferred embodiment, the external controlsystem comprises a housing containing a controller, radio transceiver,inductive charging circuit and power source. The controller is coupledto the inductive charging circuit, power source, radio transceiver, andmemory for storing information to be transmitted between the externalcontrol system and the implantable housing. The external control systemmay include a data port, such as a USB port or Bluetooth wirelessconnection, that permits the external control system to be coupled to aconventional computer, such as a personal computer or laptop computer,to configure the stimulation programs input to the stimulator and toreview and analyze data received from the stimulator.

The stimulator system further may comprise monitoring and controlsoftware, configured to run on a conventional personal computer, laptopcomputer, “smart phone” or other computational device that enables thepatient's physician to configure and monitor operation of the externalcontrol system and stimulator. The software may include routines forcontrolling any of a number of parameters associated with operation ofthe various therapeutic module circuitries incorporated in thestimulator. The software further may be configured, for example, to sendimmediate commands to the stimulator to start or stop muscle oranalgesic stimulation, to perform RF ablation, or to take a currentreading of muscle activity and adjust the stimulation regime(s), or tochange the electrodes used to apply stimulation. Finally, the softwaremay be configured to download data collected from the stimulator andstored on the external control system, such as during a patient visit tothe physician's office.

Methods of operating the stimulator system of the present invention alsoare provided. The implantable portion of the stimulator may be placedsubcutaneously using interventional radiologic techniques includingradiographic imaging or ultrasound, while the electrode leads may beplaced using surgical, percutaneous, or minimally invasive techniques.The stimulator preferably is programmed using radio frequency couplingof the transceivers in the stimulator and the external control system,while power is supplied to the battery of the stimulator by coupling theinductive charging circuits of the stimulator and external controlsystem. Additional details of methods of implanting and operating astimulator system in accordance with the present invention are describedbelow.

V. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an exemplary embodiment of a stimulatorsystem constructed in accordance with the principles of the presentinvention.

FIG. 2 is a side view of the implantable portion of the stimulatorsystem of FIG. 1.

FIG. 3 is a generalized block diagram of the stimulator of FIG. 2.

FIG. 4 is a schematic diagram of a first embodiment of the stimulator ofFIG. 3, wherein the stimulator is configured to deliver bothneuromuscular stimulation and analgesic stimulation to afferent nervefibers.

FIG. 5 is a schematic diagram of a second embodiment of the stimulatorof FIG. 3 wherein the stimulator is configured to deliver neuromuscularstimulation, monitor the effects of the applied stimulation, and adaptthe stimulation regime to improve muscle toning and reduce patientdiscomfort.

FIG. 6 is a schematic diagram of an alternative embodiment of theapparatus of the present invention that provides a selective ablationcapability.

FIG. 7 is a schematic diagram of a further alternative embodiment of thestimulator of the present invention that includes neuromuscularstimulation, pain reduction, performance feedback and selective nerveablation capabilities.

FIGS. 8A and 8B are, respectively, a plan view and detailed view of anexemplary electrode constructed in accordance with the principles of thepresent invention.

VI. DETAILED DESCRIPTION OF THE INVENTION System Overview

Referring to FIG. 1, an overview of an exemplary stimulator systemconstructed in accordance with the principles of the present inventionis provided. In FIG. 1, components of the system are not depicted toscale on either a relative or absolute basis. Stimulator system 10comprises implantable stimulator 20 and external control system 30. Inthe illustrated embodiment, software may be installed and run on aconventional laptop computer, and used by the patient's physician toprogram external control system 30 and/or to provide programming that iscommunicated by external control system 30 to stimulator 20. Duringpatient visits, external system 30 may be coupled, either wirelessly orusing a cable, to the physician's computer to download for review datastored on stimulator 20, or to adjust the operational parameters of thestimulator.

In FIG. 1 implantable stimulator 20 is connected to a plurality ofelectrode leads. Illustratively, electrode lead 21 is connected toelectrode pair 22, which is situated close to or around a peripheralnerve N where the nerve enters skeletal muscle SM, which may be amultifidus muscle. Electrode pair 22 may deliver neuromuscularelectrical stimulation (“NMES”) pulses to nerve N that inducecontraction of muscle SM to effect contraction of the muscle, andrestoration of neural control and rehabilitation of the muscle, asdescribed in the aforementioned U.S. Patent Application Publication No.US2008/0228241 to Sachs. Electrode lead 23 is illustratively disposedwith electrode pair 24 adjacent or near to peripheral nerve P, such thatelectrical stimulation may be applied to achieve pain control in theregion served by the peripheral nerves. Electrode lead 25 illustrativelyincludes quadripolar electrode array 26, which is placed near spinalcord S in a manner well known to one skilled in the art to deliverSpinal Cord Stimulation therapy that reduces or blocks the transmissionof pain signals to the patient's brain B.

Implantable stimulator 20 is controlled by, and optionally powered by,external control system 30, which communicates with stimulator 20 viaantenna 31, which may comprise an inductive coil configured to transmitpower and communicate information in a bidirectional manner across skinSK. The technology for antenna 31 is well known to one skilled in theart and may include a magnet, a coil of wire, a longer range telemetrysystem (such as using MICS), or technology similar to a pacemakerprogrammer. Alternatively, coil 30 may be used to transmit power only,and separate radio frequency transmitters may be provided in externalcontrol system 30 and stimulator 20 for establishing directional datacommunication.

Referring now to FIG. 2, an exemplary embodiment of implantablestimulator 20 coupled to electrode lead 27 is described. As is commonwith other active implantable medical devices, the stimulatorelectronics are housed in a hermetically sealed metal housing 28.Housing 28 may comprise titanium or other biocompatible material, andincludes connector block 29 that permits allows electrode lead 27 to beelectrically coupled to the electronics within housing 28. While onlyone electrode lead 27 is shown coupled to connector block 29, it shouldbe understood that multiple leads may connected to connector block 29,as shown in FIG. 1. Electrode lead 27 contains a plurality of electrodes27 a-27 d that may be used for multiple purposes, as described in detailbelow. The construction of electrode lead, the electrode design andmanufacture, and connector block 29 are all well known to those skilledin the art. As will also be understood by one of skill in the art, anelectrode lead may contain more or fewer than four electrodes, asdescribed in detail below with respect to FIGS. 8A and 8B.

With respect to FIG. 3, a generalized schematic diagram of the internalfunctional components of implantable stimulator 20 is now described.Stimulator 20 includes controller 40, telemetry system 41 coupled toantenna 42 (which may be inside or external to the hermetic housing),power supply 43, electrode switching array 44, system sensors 45, andtherapeutic circuitry modules 46 and 47. Electrode switching array 44 isselectably coupled to terminal array 48, which is housed in connectorblock 29 and enables stimulator 20 to be coupled to one or moreelectrode leads, as shown in FIG. 1.

Controller 40 may comprise a commercially available microcontroller unitincluding a programmable microprocessor, volatile memory, nonvolatilememory such as EEPROM for storing programming, and nonvolatile storage,e.g., Flash memory, for storing a log of system operational parametersand patient data. Controller 40 is coupled to telemetry system 41 thatpermits transmission of energy and data between implantable stimulator20 and external control system 30. Controller 40 also is coupled totherapeutic circuitry modules 46 and 47 that provide any of a number ofcomplimentary therapeutic stimulation, analgesic, feedback or ablationtreatment modalities as described in detail below. Controller 40 furthermay be coupled to electrode switching array 44 so that any set ofelectrodes of the electrode leads may be selectably coupled totherapeutic circuitry modules 46 and 47. In this way, an appropriateelectrode set may be chosen from the entire selection of electrodesimplanted in the patient's body to achieve a desired therapeutic effect.Electrode switching array 44 preferably operates at high speed, therebyallowing successive stimulation pulses to be applied to differentelectrode combinations.

Power supply 43 powers the electrical components of implantablestimulator 20, and may comprise a primary cell or battery, a secondary(rechargeable) cell or battery or a combination of both. Alternatively,power supply 43 may not include a cell or battery, but instead comprisea capacitor that stores energy transmitted through the skin via aTranscutaneous Energy Transmission System (TETs), e.g., by inductivecoupling. Stimulator 20 may be programmed and/or controlled by, and mayupload stored system and operational data to external control system 30via telemetry system 41. In a preferred embodiment, power supply 43comprises a lithium ion battery.

System sensors 45 may comprise one or more sensors that monitoroperation of the systems of implantable stimulator 20, and log datarelating to system operation as well as system faults, which may bestored in a log for later readout using the external control system.Sensors 45 may include, for example, a humidity sensor to measuremoisture within housing 28, which may provide information relating tothe state of the electronic components, or a temperature sensor, e.g.,for measuring battery temperature during charging to ensure safeoperation of the battery. System sensors 45 also may include a 3-axisaccelerometer for determining whether the patient is active or asleepand to sense overall activity of the patient, which may be a surrogatemeasure for clinical parameters (e.g., more activity implies less pain),and/or a heart rate or breathing rate (minute ventilation) monitor,e.g., which may be obtained using one or more of the electrodes disposedon the electrode leads. Data from the system sensors may be logged bycontroller 40 and stored in nonvolatile memory for later transmission toexternal controller 30 via telemetry system 41.

If system sensor 45 includes an accelerometer, it may be used todetermine the orientation of stimulator 20, and by inference theorientation of the patient, at any time. For example, afterimplantation, external control system 30 may be used to take a readingfrom the implant, e.g., when the patient is lying prone, to calibratethe orientation of the accelerometer. If the patient is instructed tolie prone during therapy delivery, then the accelerometer may beprogrammed to record the orientation of the patient during stimulation,thus providing information on patient compliance.

Implantable stimulator 20 illustratively includes two therapeuticcircuitry modules 46 and 47, although more or fewer circuitry modulesmay be employed in a particular embodiment depending upon its intendedapplication. As described in greater detail below with respect tofurther embodiments, therapeutic circuitry modules 46 and 47 may beconfigured to provide different types of stimulation, either to inducemuscle contractions or to block pain signals in afferent nerve fibers,to monitor muscle contractions induced by stimulation and vary theapplied stimulation regime as needed to obtain a desired result, or toselectively and intermittently ablate nerve fibers to control pain andthereby facilitate muscle rehabilitation As shown in FIG. 3, thetherapeutic circuitry modules are coupled to and controlled bycontroller 40.

Typical stimulation parameters provided for different requirements aresummarized below, and will be well known to those skilled in the art:

-   -   For neuromuscular electrical stimulation (NMES):        -   Bipolar electrode pairs        -   Biphasic rectangular charge balanced        -   0.5-500 ms pulse width (adjustable to control intensity)        -   10-30 Hz (to achieve tetanic contraction)        -   Constant current, <50 mA (<50V)    -   For PENS type stimulation:        -   Multiple bipolar electrode system        -   Biphasic pulses        -   20-40 Hz (including possibility of variable frequency over            time of application of therapy)        -   Constant current (typically 5-20 mA)    -   For Spinal Cord Stimulation:        -   Multiple electrode configurations        -   Biphasic rectangular charge balanced        -   Typically 500 μsec pulse width        -   Current control (preferred) or voltage control, typically up            to 10 mA into a 1KΩ load    -   For Radio Frequency Ablation:        -   450-500 KHz        -   RF heating energy

Embodiments comprising specific combinations of therapeutic circuitrymodules in accordance with the principles of the present invention aredescribed below.

Combination Stimulator for Neuromuscular Electrical Stimulation and PainRelief

Referring now to FIG. 4, a first embodiment of a neuromuscularelectrical stimulation is described, which provides both stimulation toimprove muscle tone and neural drive, while also providing stimulationto block or reduce transmission of pain along afferent nerve fibers. Inthe schematic of FIG. 4, implantable stimulator 50 includes controller51, telemetry system 52 coupled to antenna 53, power supply 54,electrode switching array 55, system sensors 56, and NMES circuitrymodule 57 and analgesic stimulation circuitry module 58. Electrodeswitching array 55 is selectably coupled to terminal array 59, which iscoupled to the connector block 29 (see FIG. 2) and enables stimulator 50to be coupled to one or more electrode leads.

Each of components 51 to 59 operates in the manner described above forthe embodiment of FIG. 3. More specifically, controller 51 preferablyincludes a programmable microprocessor, volatile memory, nonvolatilememory, and nonvolatile storage, and is coupled to and controlsoperation of telemetry system 52, NMES circuitry module 57, analgesicstimulation circuitry module 58, and electrode switching array 55. Powersupply 54 powers the electrical components of implantable stimulator 50,and may comprise a primary cell or battery, a secondary cell or battery,a combination of both or neither. In the latter case, power supply 54may comprise a capacitor that stores energy transmitted through the skinvia TETS. Stimulator 50 may be programmed and/or controlled by, and mayupload stored system and operational data to external control system 30via telemetry system 52. System sensors 56 may comprise one or moresensors that monitor operation of stimulator 50, as well as patientparameters, such as movement, heart rate, etc., and may log datarelating to these parameters for later readout using the externalcontrol system.

In the embodiment of FIG. 4, NMES circuitry module is configured toprovide stimulatory pulses to the nerves innervating, or directly to themuscle fiber of, the multifidus or other selected muscle group to causea predetermined series of muscle contractions in during a predeterminednumber of sessions to enhance muscle tone and improve neural drive inthe muscle, as described in the above published application to Sachs,U.S. Patent Application Publication No. US 2008/0228241, the entirety ofwhich is incorporated herein by reference.

Some patients receiving stimulator 50 may experience back pain due toprevious injury and/or loss of muscle tone, while other patients mayfind the contractions induced by operation of the NMES circuitry to beunpleasant. Accordingly, stimulator 50 further includes analgesicstimulation circuitry module 58 to block or reduce pain associated withthe previous injury or muscle contractions induced by the NMES therapy.As depicted in FIG. 1, in one preferred application of stimulator 50(corresponding to stimulator 20 in FIG. 1), electrode pair 22 issituated on the medial branch of the dorsal ramus to deliver NMES pulsesthat cause muscle contraction to effect restoration of neural drive toand rehabilitation of the multifidus muscle. Analgesic stimulationcircuitry module 58 may simultaneously be coupled to electrode pair 34,via electrode lead 23, and quad electrode 26, via electrode lead 25, toblock or reduce pain signals generated in spinal cord S or peripheralnerve P. In addition, electrode pair 22 also may be used, e.g., bycontroller 51 switching electrode switching array 55 to couple electrodepair 22 to analgesic stimulation circuitry module 58, to deliver higherfrequency stimulation to block afferent pain signals. In this manner, itis expected that NMES therapy may be provided while reducing patientdiscomfort and pain associated with any pre-existing injury.

Stimulator 50 and the electrodes also may be configured such that oneset of electrodes is used to simulate the tissues on one side of thebody, and another set of electrodes is used to simulate tissues on theother side of the body. In this manner, the stimulator and electrodesystem can be configured to deliver unilateral or bilateral stimulation,or a combination of electrodes stimulating tissues in no particulargeometric arrangement.

Alternatively, a plurality of electrodes may be implanted on or adjacentto the medial branch of the dorsal ramus, such that one pair deliversNMES via circuitry module 57 to effect contraction of the multifidusmuscle, and another pair simultaneously or successively delivers higherfrequency stimulation via circuitry module 58 to block the pain signalsin the afferent fibers. The pairs of electrodes may include one or morecommon electrodes. The timing of the different electrical stimulationdelivered offers several options. For example, the pain blockingstimulation may occur simultaneously with the NMES stimulation, may bemultiplexed with the NMES stimulation (i.e., time wise interleaved sothat stimulation pulses are not delivered simultaneously on bothelectrode pairs), in an alternating manner (i.e., NMES then painblocking and so on), or episodically, such as NMES for a period withoutpain blocking stimulation, and then pain blocking stimulation when theNMES is not being delivered.

In a preferred embodiment intended for clinical applications, NMESstimulation is applied to the multifidus in sessions, typically one hourper day over a period of a few weeks. Such a regime is similar toconventional strength training by physical exercise which typicallyfollows a similar time course. In preparation for the sessions of NMESstrength training, stimulator 50 may be used to apply SCS therapy toblock or dampen the pain signals which may arise from the NMES exerciseregime. In this way, the desired therapeutic effect of restoration ofneural drive and rehabilitation of the multifidus may occur withoutsubstantial pain or discomfort. For patients afflicted with severe backor radicular pain, stimulator 50 offers the capability to apply SCStherapy at the same time as NMES rehabilitation therapy for themultifidus.

In one embodiment, the patient may have access to external controlsystem 30, and can thus activate implantable stimulator 50 in accordancewith a rehabilitation plan developed jointly with his or her physician.In this case, controller 51 may be programmed to provide a delay ofspecified duration between activation of the stimulator and initiationof the stimulation pulses. This delay allows the patient to assume acomfortable position before the stimulation is applied, e.g., by lyingprone. The external control system also may include a multi-functionaluser interface, including a range of patient operated inputs (e.g.,buttons, knobs, touch screen, etc.) that allows activation or suspensionof different types of stimulation.

In another embodiment, implantable stimulator 50 may be programmed toramp up and ramp down the strength and duration of the stimulationpulses. This can be done in at least one of two manners. In the firstmanner, the stimulation pulse intensity is increased gradually (e.g.,over 0.5 to 1 second) to a programmed maximum value to elicit thedesired muscle contraction and then ramped down slowly. In this way, themuscle contraction has a smooth on and off sensation for the patient. Inthe second manner, the therapeutic dose (i.e., the number ofcontractions of a therapy period) are programmed to increase graduallyuntil the desired level is achieved and then decrease gradually to zero,in much the same way that a good muscle strength training regimeprovides a stretching or warm-up phase and cool-down phase. In this modeof operation, stimulator 50, via either input to the external controlsystem or at a pre-determined time, and following the stimulation delay(if any), ramps us the stimulation amplitude from a low level (e.g.,beginning at zero) to a pre-determined maximum level over apre-determined period of time. Likewise, upon conclusion of thestimulation therapy period, stimulator 50 ramps the amplitude down fromthe pre-determined maximum level to a low level. It is expected thatthis embodiment, which provides a gradual increase and decrease ofstimulation intensity, will provide a more comfortable experience forsome patients.

As discussed above, implantable stimulator 50 preferably containsnonvolatile memory for storage, and is programmed to log data during thetherapy session, along with internal parameters of the device. Such datalogging may also record data from system sensors 56, which may bedownloaded from stimulator 50 using the external control system, toprovide an indication of the effectiveness of the therapy. For example,if the sensors include a three axis accelerometer, then a patient'soverall activity level on an hourly, daily, or weekly basis may belogged, for example, by recording an integral of all accelerometermeasurements. The sensors also may include circuitry for determiningheart rate, and such circuitry may be used to record the patient'smaximum heart rate as a measure of overall activity.

In clinical use, the stimulator 50 is implanted subcutaneously, andsystem sensors 55 may be used to record and log baseline (i.e.,pre-therapy) patient parameters such as total activity and maximum heartrate. The therapy then is enabled, and the data logging may be used toassess progress of the therapy and the patient's change in status. Forexample, if the accelerometer shows increased overall activity, thiswould indicate that the pain, which was previously inhibiting activity,had been ameliorated. Such data may be used by the physician to adjustthe therapy by adjusting the programming of stimulator 50 using externalcontrol system 30, and/or such information may be provided to thepatient as encouraging feedback.

Stimulator for Neuromuscular Stimulation with Performance Feedback

Referring now to FIG. 5, another embodiment of a stimulation systemconstructed in accordance with the principles of the present inventionis described, in which the implantable stimulator provides a NMESstimulator therapy and further has the capability to monitor theprogress of the therapy and to revise the therapy regime to reflectchanges in the muscle characteristics resulting from the therapy. Suchrevision may be made by way of a physician periodically reprogrammingthe NMES parameters using external control system 30, or alternativelythe NMES stimulation parameters may be adjusted dynamically andautomatically modified to keep the muscle contraction at a certainpredetermined efficacious and tolerable level. In some embodiments,stimulator 60 may provide a closed loop feedback system, in which thesystem instantaneously responds to physiological changes affecting thestimulation characteristics of the muscle.

Although a primary application of the inventive technology is to improvestability of the spine, it also may be advantageously applied in otherareas of muscle rehabilitation, e.g.:

-   -   Restoration of function of leg muscles to allow standing and        walking in paraplegic patients (referred to as Functional        Electrical Stimulation (FES));    -   Rehabilitation of injured or weakened muscles following surgery        or correction of osteoarthritis, such as rehabilitation of the        quadriceps after knee surgery;    -   Restoration of neural drive and rehabilitation of muscles that        are part of the stabilizing system in the back, including the        lumbar multifidus;    -   Providing stimulation to effect breathing (diaphragm and/or        intercostal muscles); and    -   Providing mechanical muscle power to perform a bodily function,        for example, as in cardiomyoplasty.

The implantable NMES stimulator described in the above-incorporatedSachs application discusses that the parameters for electricalstimulation may be programmed into the stimulator following testing bythe physician of stimulation thresholds. Therapy parameters such asduration, frequency and strength of contraction also may be programmedinto the stimulator according to the patient's needs, and the stage oftherapy delivery. In some cases it is expected that the programmedparameters may need to be changed, for example during the course of thetherapy program as the muscle becomes rehabilitated.

Stimulator 60 of FIG. 5 is designed to improve the NMES performance andreduce the need for frequent reprogramming by monitoring muscleperformance during therapy, and adjusting the stimulation parametersaccordingly. More specifically, implantable stimulator 60 includescontroller 61, telemetry system 62 coupled to antenna 63, power supply64, electrode switching array 65, system sensors 66, and NMES circuitrymodule 67 and muscle performance monitoring circuitry module 68.Electrode switching array 65 is selectably coupled to terminal array 69,which is coupled to the connector block 29 (see FIG. 2) and enablesstimulator 60 to be coupled to one or more electrode leads. Electrodeswitching array 65 also may include connection 69 a to the housing ofstimulator 60, so that the housing functions as an electrode.

Each of components 61 to 67 and 69 operates in the manner describedabove for the embodiment of FIG. 3. Controller 61 preferably includes aprogrammable microprocessor, volatile memory, nonvolatile memory, andnonvolatile storage, and is coupled to and controls operation oftelemetry system 62, NMES circuitry module 67, muscle performancemonitoring circuitry module 68, and electrode switching array 65. Powersupply 64 powers the electrical components of implantable stimulator 60,and may comprise a primary cell or battery, a secondary cell or battery,a combination of both or neither. In the latter case, power supply 64may comprise or include a capacitor that stores energy transmittedthrough the skin via a Transcutaneous Energy Transmission System(“TETS”). Stimulator 60 may be programmed and/or controlled by, and mayupload stored system and operational data to external control system 30via telemetry system 62. System sensors 66 may comprise one or moresensors that monitor operation of stimulator 60, as well as patientparameters, such as movement, heart rate, etc., and may log datarelating to these parameters for later readout using the externalcontrol system.

In accordance with one aspect of the present invention, stimulator 60further comprises muscle performance monitoring circuitry module 68coupled to controller, and designed to monitor one or more parameters ofmuscle performance. The measured parameters may be used to automaticallymodify the therapy delivered by NMES circuitry module 67, and/or toprovide stored and telemetered information via telemetry system 62 andexternal control system 30 that enable the physician to modify theparameters. In one preferred embodiment, muscle performance monitoringcircuitry module 68 may be coupled through electrode switching array 65to selected electrodes coupled to terminal array 69 to measureelectrical parameters of the tissue, such as impedance, or evokedpotential from the stimulation. Circuitry module 68 may in addition becoupled to system sensor 66, for example, to obtain data from anaccelerometer or other movement transducer, and/or temperature orpressure. Circuitry module 68 also may be configured to receive inputsfrom other types of body sensors such as are known in the art, includingthose monitoring chemical properties (e.g., pH sensor, etc.). Circuitrymodule 68 preferably includes at least one listening amplifierconfigured for electromyography (EMG). EMG is an electrical signalproduced by muscle when it contracts, and the strength (power) of theEMG is an indicator of strength of muscle contraction. Configuration ofan amplifier for measurement of EMG, e.g., gain, frequency response,impedance, etc., is well known to those skilled in the art. As describedin Stokes, Ian A F, Sharon M Henry, and Richard M Single, “Surface EMGelectrodes do not accurately record from lumbar multifidus muscles,”Clinical Biomechanics (Bristol, Avon) 18, no. 1 (January 2003): 9-13, itis known that certain muscles, such as the deep fibers of the lumbarmultifidus, surface EMG provides an unreliable signal. Accordingly, theimplantable electrode leads used with stimulator 60 advantageously areexpected to provide a useful EMG signal.

In another embodiment, circuitry modules 67 and 68 may be configured toperform impedance measurements, in a manner similar to that described inU.S. Pat. No. 6,406,421 B1 to Grandjean et al. As is well known, anelectrical impedance measurement may be performed by injecting a currentthrough one pair of electrodes, and measuring voltage through adifferent pair of electrodes disposed approximately along the samegeometric path. See, e.g., Rutkove, S. B., “Electrical impedancemyography: Background, current state, and future directions”, Muscle &Nerve 40, No. 6 (December 2009): 936-46. In one implementation, a firstpair of electrodes consisting of the stimulator housing (via connection69 a) and one or more of electrodes disposed on an electrode lead may beused to inject current into the tissue (e.g., from NMES circuitry module67), while voltage is measured by circuitry module between thestimulator housing and a different set of one or more of electrodes onthe electrode leads. Alternatively, the same set of electrodes(including the stimulator housing) may be used for both injectingcurrent and measuring the resulting voltage.

The foregoing impedance measurements may be of direct current (DC) oralternating current (AC). With AC impedance measurement, additionaluseful information may be obtained such as phase, frequency spectrum,and changes in parameters. The electrical impedance so measured is anindication of the tissue volume and tissue organization (anisotropy)between the measurement electrodes, as reported in Garmirian et al.,“Discriminating neurogenic from myopathic disease via measurement ofmuscle anisotropy”, Muscle Nerve, 2009 January; 39 (1): 16-24. See also,Miyatani, M., et al., “Validity of estimating limb muscle volume bybioelectrical impedance”, J. Applied Physio. (Bethesda, Md. 1985) 91,no. 1 (July 2001): 386-94. Accordingly, judicious placement of theelectrodes and the stimulator housing will ensure that only the tissueof interest (e.g., the target muscle) is in the path of the injected andmeasured voltage. As a muscle contracts, its dimensions change, and thiswill generate a change in electrical impedance. Thus, measurement ofelectrical impedance may be used as a surrogate measure of musclecontraction.

In another embodiment, circuitry module 68 may include or be coupled toa transducer that senses mechanical motion, such as vibration,acceleration or deflection, and may include piezoelectric polymers(e.g., PVDF) placed on a lead. The signal from such a transducerprovides a surrogate measure of muscle contraction. In a furtheralternative embodiment, circuitry module 68 may include or be coupled toa transducer that senses pressure, such as a MEMS pressure sensorsdisposed on a lead, and which thus provides a surrogate measure ofmuscle contraction.

In yet another embodiment, stimulator 60 is configured to sense EMG frommore than one muscle, using multiple electrode leads or multipleelectrodes on a single lead that passes through more than one muscle. Inthis case, the listening amplifier of circuitry module 68 is multiplexedto listen for EMGs from more than one muscle. Alternatively, circuitrymodule 68 may include multiple listening amplifiers that are arranged tosimultaneously listen to EMGs from more than one muscle. It iswell-known, for example from Jaap van Dieen et al., “Trunk MuscleRecruitment Patterns,” Spine Vol. 28, Number 8 pg 834-841, that therelative timing and amplitude of EMGs in trunk muscles during theperformance of specific tasks is different between healthy individualsand patients experiencing low back pain due to spinal instability. Inpatients with spinal instability, recruitment patterns of the trunkmuscles may be altered to compensate for the lack of spinal stability.The amplitude and timing of EMGs measured from multiple trunk musclestherefore may be used to diagnose the presence and degree of spinalinstability, as well as the change of spinal instability during a courseof therapy. The EMG data may be used to automatically modify treatmentparameters, or such data may be stored for later review by the physicianto assist in diagnosis and revision of the therapy parameters.

In the embodiment of FIG. 5, muscle performance monitoring circuitrymodule 68 is configured to measure muscle contraction induced by NMEScircuitry module 67, and to modify the therapeutic parameters as muscleperformance changes. In particular, the initial therapeutic parameters,such as dose and duration of therapy session, are established andprogrammed into stimulator 60 using external control system 30. Betweentherapy sessions, muscle performance may be monitored continuously orperiodically using circuitry module 68. When the change in measuredmuscle performance exceeds a predetermined physician selected threshold,circuitry module 68 may instruct controller 61 to modify the parametersfor subsequent NMES therapy sessions. For example, if the monitoringparameters reveal that the muscle mass has increased, indicative ofmuscle rehabilitation, or contractility has decreased, then the therapydose may be automatically reduced some pre-determined amount aspreviously programmed by the physician.

In an alternative embodiment, muscle performance may be used to inhibitmuscle contraction. For example, in certain types of low back pain, painis caused by spasm of certain muscles in the back. Such spasm isaccompanied by continuous increase in EMG activity. In accordance withone aspect of the present invention, NMES stimulation may be used toinhibit muscle contraction by configuring the listening amplifier ofcircuitry module 68 to continuously or periodically measure EMG. If theEMG satisfies conditions indicating that muscle spasm has occurred, thenNMES circuitry module is directed by controller 61 to apply stimulationto the nerve innervating the muscle in spasm to block conduction ofsignals from the nervous system which cause the muscle spasm, therebypreventing spasm. The stimulation provided by NMES circuitry module maybe inhibited from time to time to allow circuitry module 68 to assessfrom the EMG signal if the muscle is still in spasm; if spasm hasceased, then application stimulation by NMES circuitry module 67 isterminated.

In an alternative embodiment, muscle performance monitoring circuitrymodule 68 may be configured to measure a combination of EMG and tissueimpedance to confirm that a muscle is in spasm, thereby improving thesafety and reliability of the measurement. Muscle performance monitoringcircuitry module 68 also may be used to track changes in activity andhealth of the muscle in response to neural activity. In other words, theamount of muscle contraction as determined by impedance measurement oftissue volume may be correlated to the amount of electrical activity inthe muscle as determined by EMG. Further still, the electrodes andmuscle performance monitoring circuitry module 68 may be configured torecord electrical signals from the nerves as well as the muscle, suchthat a measurement of the EMG (and/or tissue volume) in response toneural activity may be used as an indication of the health of themuscle.

Muscle performance monitoring circuitry module 68 also may employmeasurement of the change in muscle mass in response to NMES of thenerve to adjust the electrical stimulation parameters. In this case, anempirically derived transfer function may be determined that relateselectrical stimulation parameters, such as current, pulse width,frequency and duration, to the strength of contraction of the muscle.Over time, this transfer function may change, for example, as a resultof electrode changes from movement or tissue ingrowth. Thus, thestrength of muscle contraction may be used to automatically adjust theelectrical parameters of the NMES stimulation provided by circuitrymodule 67 to achieve a desired muscle contraction.

Stimulator with RF Ablation Capability

Referring to FIG. 6, in accordance with another aspect of the presentinvention, an implantable RF ablation device is described. Although aprimary application of the inventive technology is pain reduction inconnection with improving stability of the spine, the inventivetechnology may be advantageously applied in other areas, for example:

-   -   RF rhizotomy, in which a sensory nerve is ablated to prevent        sensory signals (e.g., pain) from reaching the brain, such as        rhizotomy of the medial branch of the dorsal ramus in patients        with facet joint pain;    -   RF ablation of unresectable tumors located in the liver, brain,        musculoskeletal system, thyroid and parathyroid glands,        pancreas, kidney, lung, and breast, in which it is difficult to        achieve complete tumor necrosis, leading to recurrence of the        tumors and necessitating repeated RF ablation; and    -   Treatment of tumors in which the root of the tumor is located in        tissue that is considered too risky for surgical intervention,        such as tumors with roots in the digestive tract, uterine wall        or certain oesophageal tumors, and for which regular repeat        surgery is required to remove new growths.

The field of RF ablation is well developed, and parameters suitable forablating nerve fibers and other tissues, such as RF energy, andattendant issues is well known to those of ordinary skill in the art.See, e.g., Gazelle et al., “Tumor ablation with radio-frequency energy”,Radiology, December 2000: 217 (3): 633-46 and Haemerrich et al, “Thermaltumour ablation: devices, clinical applications and future directions”,Int. J. Hyperthermia, 2005 December; 21 (8):755-60. To the inventors'knowledge, however, no one has suggested an RF ablation device that isconfigured to be chronically implanted and capable of performingrepeated RF ablation.

Referring now to FIG. 6, implantable device 70 is described, which isintended for chronic implantation to perform serial RF ablations inscenarios where it is necessary to repeat RF ablation of tissue in aparticular region of the body after certain periods of time. Thecomponents of device 70 correspond closely to those described above withrespect to the embodiment of FIG. 3, and includes controller 71,telemetry system 72 coupled to antenna 73, power supply 74, electrodeswitching array 75, system sensors 76, and terminal array 77. As in thepreceding embodiments, electrode switching array 75 is selectablycoupled to terminal array 77, which is coupled to the connector block 29(see FIG. 2) that accepts one or more implantable electrode leads.Electrode switching array 75 also may include connection 77 a to thehousing of device 70, so that the housing functions as an electrode. Inaccordance with this aspect of the present invention, device 70 furthercomprises RF ablation circuitry module 78, as further described below.

Each of components 71 to 77 operates in the manner described above forthe embodiment of FIG. 3. Controller 71 preferably includes aprogrammable microprocessor, volatile memory, nonvolatile memory, andnonvolatile storage, and is coupled to and controls operation oftelemetry system 72, electrode switching array 75 and RF ablationcircuitry module 78. Power supply 74 powers the electrical components ofdevice 70, and may comprise a primary cell or battery, a secondary cellor battery, a combination of both, or neither. In the latter case, powersupply 74 may comprise or include a capacitor (such as a super capacitorof technology known to those skilled in the art) that stores energytransmitted through the skin via TETS. Device 70 may be programmedand/or controlled by, and may upload stored system and operational datato external control system 30 via telemetry system 72. System sensors 76may comprise one or more sensors that monitor operation of device 70, aswell as patient parameters, such as tissue impedance, and may log datarelating to these parameters for later readout using the externalcontrol system.

In accordance with this aspect of the present invention, device 70further comprises RF ablation circuitry module 78 coupled to controller,and designed to periodically ablate tissue or nerve fibers using RFenergy. Accordingly, controller 71 may be configured to controloperation of the telemetry system 72 to receive energy wirelessly fromexternal control system 30 and store that energy in power supply 74, andmay be configured to communicate the amplitude of received power back tothe external control system via telemetry system 72 or via modulation ofthe impedance of the antenna 73. To ensure that RF ablation is onlycarried out at the direction of the external control system, device 70may not include battery or capacitor, but instead may be arranged sothat it is energized only when in communication with the externalcontrol system.

Expected energy requirements for the RF ablation circuitry module are ina range of about 1-40 watts, depending upon the intended application.TETS systems with this power capacity are well known to those skilled inthe art and have been used, for example, with artificial hearts or LeftVentricular Assist Devices (LVADs). However, the physical volume andother requirements of a high power TETS system may preclude its use inapplications where the available surgical locations are limited. Thus,in an alternative embodiment, the TETS system may be of lower powercapacity than the requirements of the RF generator, and device 70 mayinclude an energy storage element, such as a super capacitor or lowimpedance secondary (rechargeable) cell, for powering RF ablationcircuitry module 78. In use, the TETS may operate continuously, suchthat a signal is generated when there is adequate energy stored in theimplantable device to deliver the RF ablation energy at the desiredpower and for the desired time. As an example, a TETS system capable oftransferring 1 W may be used to supply RF energy delivery of 5 W with20% duty cycle.

In this embodiment, telemetry system 72 enables communications betweenthe external control system and device 70, allowing the implantabledevice to receive device and RF ablation operating parameters, as wellas communicate logged information such as impedance between electrodes,temperature data and battery status to the external control system.Telemetry system 71 also may provide programming to controller 71 toreconfigure the operative electrodes through which ablation energy issupplied using electrode switching array 75, thereby allowing anyelectrode of a plurality of electrodes to be configured as a cathode, ananode or unconnected. The housing of device 70 also may be configured asan electrode via connection 77 a of terminal array 77. The foregoingcapabilities provide flexibility in the location of ablation lesions andallow the physician to compensate for electrode movement afterimplantation.

System sensors 76 advantageously may be used to monitor the temperatureof the tissue near the electrodes thru which energy for ablation isdelivered. Typical tissue temperatures for RF ablation range from 50 Cto 130 C, depending on the type of tissue being ablated and the timeallocated to the ablation. System sensors 76 may comprise, e.g.,temperature sensors disposed within the device housing, or alternativelymay measure the temperature of the connection to the electrode leads,and use that data to infer or predict the tissue temperature.Temperature sensors may also be incorporated into the leads and placedcloser to the tissue targeted for ablation. System sensors 76 may beused in a passive (measuring) mode, or alternatively may comprise partof a feedback control system that continually or intermittently adjustspower delivered by the RF ablation circuitry module so that thetemperature of the ablated tissue is maintained between desired limitsfor safety and efficacy.

Referring now to FIG. 7, an implantable stimulator illustrativelyincorporating all of the therapeutic circuitry modules described for thepreceding embodiments is described. Implantable stimulator 80corresponds to stimulator 20 of FIG. 1, and is programmed and controlledand/or powered by external control system 30. Stimulator 80 is intendedfor use, for example, in a stimulator that provides NMES stimulation,analgesic stimulation to block or reduce afferent pain signals in anerve, and permits periodic nerve ablation (such as rhizotomy). Furtherin accordance with this aspect of the present invention, stimulator 80includes muscle performance monitoring circuitry that supports testingof nerve fibers prior to rhizotomy, which to guide proper selection ofthe ablation electrodes.

Stimulator 80 of FIG. 7 includes controller 81, telemetry system 82coupled to antenna 83, power supply 84, electrode switching array 85,system sensors 86, terminal array 87, NMES circuitry module 88,analgesic stimulation circuitry module 89, muscle performance monitoringcircuitry module 90, and RF ablation circuitry module 91. As in thepreceding embodiments, electrode switching array 85 is selectablycoupled to terminal array 87 under the control of controller 81, andenables any one or more of the therapeutic circuitry modules ofstimulator 80 to be selectably coupled to selected electrodes of one ormore electrode leads. Electrode switching array 85 also may includeconnection 87 a to the housing of stimulator 80, so that the housingalso may serve as an electrode.

Each of components 81 to 87 operates in the manner described above forthe embodiment of FIG. 3. Controller 81 preferably includes aprogrammable microprocessor, volatile memory, nonvolatile memory, andnonvolatile storage, and is coupled to and controls operation oftelemetry system 82, electrode switching array 85, NMES circuitry module88, analgesic stimulation circuitry module 89, muscle performancemonitoring circuitry module 90, and RF ablation circuitry module 91.Power supply 84 powers the electrical components of implantablestimulator 80, and may comprise a primary cell or battery, a secondarycell or battery, a combination of both, or neither, as discussed above.Stimulator 80 may be programmed and/or controlled by, and may uploadstored system and operational data to external control system 30 viatelemetry system 82. System sensors 86 may comprise one or more sensorsthat monitor operation of stimulator 80, as well as various patientparameters as discussed above.

In accordance with this aspect of the present invention, stimulator 80further comprises NMES circuitry module 88 and analgesic stimulationcircuitry module 89, as described above with respect to the embodimentof FIG. 4, muscle performance monitoring circuitry module 90 asdescribed above with respect to the embodiment of FIG. 5, and RFablation circuitry module 91 as described above with respect to theembodiment of FIG. 6. In this manner, a patient in need of spinal musclerehabilitation and restoration of neural drive may have the full rangeof therapeutic modalities available. In particular, stimulator 80 asinitially implanted by the physician, may be programmed to provide NMESstimulation and stimulation to block pain signals in afferent nerves. Asmuscle strength and contractility improve over the course of thetherapy, the muscle performance monitoring circuitry module 90 maymeasure the progress of the therapy and adjust the NMES stimulationparameters or circumvent spasm. In addition, depending upon thepatient's reported condition and measurement data provided by the muscleperformance monitoring circuitry module 90, the physician mayperiodically activate RF ablation circuitry module 91 to denervateselected nerve fibers.

Electrode Lead Systems

In view of the capabilities of the various implantable stimulatorsdescribed herein, it may be advantageous to provide an electrode leadspecially configured for use with such stimulators. Referring to FIGS.8A and 8B, electrode leads configured to provide NMES stimulation to anerve to cause muscle contraction; to stimulate a nerve to inhibit painsignals from propagating to the brain; to stimulate a nerve to inhibitmotor nerve signals thereby reducing or stopping contraction of a muscle(e.g., in spasm); to record electrical signals such as electromyographyor tissue impedance; or for performing in situ RF ablation are nowdescribed.

With respect to FIG. 8A, electrode lead 100 carrying electrodes 101 a to101 f is described. The number of electrodes may be as few as 1 and asmany as may be realistically placed within the target anatomical space.Electrode configurations commonly used in the art include 1 (forunipolar stimulation), 2, 4 (peripheral nerve stimulation), 8, 16(spinal cord stimulators) or up to 22 electrodes (cochlear implants).For the purpose of this disclosure, distal-most electrode 101 a will bereferred to as electrode #1, electrode 101 b will be electrode #2 and soon moving proximally along lead 100 up to the total number ofelectrodes.

When employed with an implantable stimulator as described herein thatprovides multiple independent current outputs, electrode lead 100 iscapable of delivering multiple therapies simultaneously, in an overlaidfashion or staggered. Electrodes 101 a to 101 f may be sized andpositioned relative to each other to allow for generation of a voltagefield tailored to the specific type of stimulation, sensing or ablationdesired for the given therapies.

In one embodiment, electrode lead 100 is placed parallel to a targetnerve in a caudal to cranial orientation (with the cranial directionbeing the direction tending towards afferent neural activity). Then sopositioned, electrodes 1 and 2, which are most cranial, may be sized andspaced to allow for optimal blocking of afferent pain signals beingtransmitted along the nerve (for example the pain signals being carriedfrom the facet joint along the medial branch). More caudally, electrodes3 and 4 may be sized and spaced to allow for optimal recruitment oflarge fiber motor neurons. Because the action potentials required foractivation of a muscle travel efferently, these potentials are notblocked by the more cranial blocking action of electrodes 1 and 2.Finally, electrodes 5 and 6, placed most caudally, may be sized andpositioned for sensing and recording of muscle recruitment throughcapturing the EMG signal of the muscle, which may be processed, forexample, by the muscle performance monitoring circuitry module asdescribed above with respect to the embodiment of FIG. 4. Such anarrangement therefore allows for simultaneous blocking of pain arisingfrom the facet joint, stimulation of the motor fibers of the nerveeliciting muscle contraction, and sensing of the elicited response(which would enable a closed loop system, improving device longevity andrecruitment efficiency) without any of the stimulation pulses negativelyimpacting the performance of the others.

With respect to FIG. 8B, alternative electrode lead 110 carryingelectrodes 111 a to 111 g is described. Distal-most electrode 111 aagain will be referred to as electrode #1, electrode 111 b will beelectrode #2 and so on moving proximally along lead 111. In theembodiment of FIG. 8B, a blocking action of electrodes 1 and 2 may beused to mute the sensory perception of stimulation. In this manner, NMESstimulation therapy of the motor fibers in patients may be achievedwhere the patients would otherwise not tolerate the stimulation becauseof the resulting bi-directional action potential generated by neuralstimulation. It also may be possible to use electrodes 5 and 6, whichwill likely be placed intramuscularly, to record the volume EMG signalin the muscle. Changes in this signal over time may provide anindication of the degree to which motor control has been compromised dueto injury. When such data are compared over time during the period aftera therapy regime has been completed, the data may be used as a positiveindicator that additional therapy may be required to maintain spinalstability.

While various illustrative embodiments of the invention are describedabove, it will be apparent to one skilled in the art that variouschanges and modifications may be made therein without departing from theinvention. The appended claims are intended to cover all such changesand modifications that fall within the true spirit and scope of theinvention.

What is claimed:
 1. A system for rehabilitating or aiding rehabilitationof spinal stability, the system comprising: at least one electrode leadcomprising at least one electrode, the at least one electrode leadconfigured to be implanted in or adjacent to tissue associated with atleast one muscle supporting stability of a spine; one or more sensorsconfigured to measure one or more parameters of muscle performance; anda stimulator operatively coupled to the at least one electrode lead andthe one or more sensors, the stimulator configured to: deliverelectrical stimulation to the tissue via the at least one electrode inaccordance with programmed electrical stimulation parameters to causethe at least one muscle supporting stability of the spine to contract;monitor the one or more parameters of muscle performance via the one ormore sensors to generate an output; determine an empirically derivedtransfer function based on the output that relates the programmedelectrical stimulation parameters to strength of contraction of the atleast one muscle supporting stability of the spine; and automaticallyadjust the programmed electrical stimulation parameters responsive tothe output based on the empirically derived transfer function to adjustcontraction of the at least one muscle supporting stability of thespine.
 2. The system of claim 1, wherein the stimulator is configured tomonitor one of the one or more parameters of muscle performance bymonitoring an evoked potential.
 3. The system of claim 1, wherein thestimulator is configured to monitor one of the one or more parameters ofmuscle performance by electromyography.
 4. The system of claim 1,further comprising a controller operatively coupled to or a part of thestimulator, the controller configured to diagnose a degree of spinalinstability based on the output of the one or more sensors.
 5. Thesystem of claim 4, wherein the controller is further configured todiagnose a change of spinal instability during a course of a therapy. 6.The system of claim 1, wherein the stimulator is configured to monitorone of the one or more parameters of muscle performance by monitoringtissue impedance.
 7. The system of claim 1, wherein the stimulator isconfigured to monitor one of the one or more parameters of muscleperformance by monitoring mechanical motion of the at least one musclesupporting stability of the spine.
 8. The system of claim 1, wherein thestimulator is configured to monitor one of the one or more parameters ofmuscle performance by monitoring electrical parameters of the tissueassociated with the at least one muscle supporting stability of thespine.
 9. The system of claim 1, wherein the stimulator is configured tochange the empirically derived transfer function over time.
 10. Thesystem of claim 1, wherein the stimulator is configured to continuouslymonitor the one or more parameters of muscle performance via the one ormore sensors.
 11. The system of claim 1, wherein the stimulator isconfigured to periodically monitor the one or more parameters of muscleperformance via the one or more sensors.
 12. The system of claim 1,wherein the stimulator comprises a first circuitry module operativelycoupled to the at least one electrode lead, the first circuitry moduleconfigured to deliver the electrical stimulation to the tissue via theat least one electrode in accordance with the programmed electricalstimulation parameters to cause the at least one muscle supportingstability of the spine to contract.
 13. The system of claim 12, whereinthe stimulator comprises a second circuitry module operatively coupledto the one or more sensors, the second circuitry module configured togenerate the output.
 14. The system of claim 13, wherein the secondcircuitry module is further configured to automatically adjust theprogrammed electrical stimulation parameters responsive to the output.15. The system of claim 1, wherein the stimulator is configured toautomatically adjust the programmed electrical stimulation parametersresponsive to a detected change in muscle performance.
 16. The system ofclaim 15, wherein the stimulator is configured to automatically adjustthe programmed electrical stimulation parameters when the detectedchange in muscle performance falls outside a predetermined threshold.17. The system of claim 16, wherein the detected change in muscleperformance is indicative of muscle rehabilitation, and wherein thestimulator is configured to automatically adjust the programmedelectrical stimulation parameters by a predetermined amount responsiveto the muscle rehabilitation.
 18. The system of claim 16, wherein thedetected change in muscle performance is indicative of decreased musclecontractility, and wherein the stimulator is configured to automaticallyadjust the programmed electrical stimulation parameters by apredetermined amount responsive to the decreased muscle contractility.19. The system of claim 16, wherein the detected change in muscleperformance is indicative of increased muscle contractility, and whereinthe stimulator is configured to automatically adjust the programmedelectrical stimulation parameters by a predetermined amount responsiveto the increased muscle contractility.
 20. The system of claim 16,wherein when the detected change in muscle performance falls outside ofthe predetermined threshold, additional therapy is required.
 21. Thesystem of claim 1, wherein the at least one electrode is configured tobe implanted in or adjacent to a dorsal ramus nerve innervating amultifidus muscle supporting stability of the spine, and wherein thestimulator is configured to deliver electrical stimulation to the dorsalramus nerve via the at least one electrode to cause the multifidusmuscle to contract, and the one or more sensors are configured tomonitor contraction of the multifidus muscle.
 22. A method forrehabilitating or aiding rehabilitation of spinal stability, the methodcomprising: delivering electrical stimulation to tissue associated withat least one muscle supporting stability of a spine via an electrodelead comprising at least one electrode in accordance with programmedelectrical stimulation parameters to cause the at least one musclesupporting stability of the spine to contract; monitoring one or moreparameters of muscle performance via one or more sensors; generating anoutput based on the one or more parameters of muscle performance;determining an empirically derived transfer function based on the outputthat relates the programmed electrical stimulation parameters tostrength of contraction of the at least one muscle supporting stabilityof the spine; and automatically adjusting the programmed parametersresponsive to the output based on the empirically derived transferfunction to adjust contraction of the at least one muscle supportingstability of the spine.
 23. The method of claim 22, wherein monitoringthe one or more parameters of muscle performance via the one or moresensors comprises monitoring the one or more parameters of muscleperformance via the one or more sensors continuously or periodically.24. The method of claim 22, wherein monitoring the one or moreparameters of muscle performance via the one or more sensors comprisesmonitoring electrical parameters of tissue associated with the at leastone muscle supporting stability of the spine.
 25. The method of claim22, wherein monitoring the one or more parameters of muscle performancevia the one or more sensors comprises monitoring muscle contractioninduced for the at least one muscle supporting stability of the spine.26. The method of claim 22, wherein automatically adjusting theprogrammed electrical stimulation parameters responsive to the outputcomprises automatically adjusting the programmed electrical stimulationparameters responsive to a detected change in muscle performance. 27.The method of claim 26, wherein automatically adjusting the programmedelectrical stimulation parameters responsive to a detected change inmuscle performance comprises automatically adjusting the programmedelectrical stimulation parameters when the detected change in muscleperformance falls outside a predetermined threshold.
 28. The method ofclaim 27, wherein the detected change in muscle performance isindicative of muscle rehabilitation, and wherein automatically adjustingthe programmed electrical stimulation parameters responsive to detectedchanges in muscle performance comprises automatically adjusting theprogrammed electrical stimulation parameters responsive to the musclerehabilitation.
 29. The method of claim 27, wherein the detected changein muscle performance is indicative of decreased muscle contractility,and wherein automatically adjusting the programmed electricalstimulation parameters responsive to detected changes in muscleperformance comprises automatically adjusting the programmed electricalstimulation parameters responsive to the decreased muscle contractility.30. The method of claim 27, wherein the detected change in muscleperformance is indicative of increased muscle contractility, and whereinautomatically adjusting the programmed electrical stimulation parametersresponsive to detected changes in muscle performance comprisesautomatically adjusting the programmed electrical stimulation parametersresponsive to the increased muscle contractility.